Find a antibody against a neuronal marker like NeuN, some NMDA receptor subtype, or syaptic protein. Or inject the cell with lucifer yellow or neurobiotin (followed by fluorescent labeled streptavidin) to reveal the neuronal morphology.

I found the forum today so i hope you have solved your problem since August. nevertheless, on frozen slices of rat brain, I had very good results with the anti-glutamate transporter EAAC1; The rabbit antibody is available through Alpha diagnostic (San Antonio TX). It works wonderfully at least up to 1:1000. It allows you to identify cells able to transport glutamate. Morphology and location should help you to identify pyramidal cells, since gabaergic interneurons will also label (to a lesser extent though), gaba being synthesized from glutamate . This you can discriminate by doing in parallel a slide with the anti-GAD-67 (careful! the cytoplasmic isoform!) from chemicon. you can also try co-labeling, the anti-GAD is a monoclonal.
Both antibodies will work with PAF fixation+ triton perm.
hope this help